From: Robert Klemme <bob.news@...>
Date: 2005-06-13T16:15:31+09:00
Subject: Re: Only if the object exists

Douglas Livingstone wrote:
> On 6/12/05, Mark Hubbart <discordantus@gmail.com> wrote:
>> IMHO, it wouldn't be a "heavy language modification" (irrespective of
>> the work required). I've always felt uncomfortable with the fact that
>> an assignment in a statement modifier doesn't show up for the
>> statement it is modifying, even though it is executed first. I feel
>> the following two examples should be equivalent:
>>
>>   if t = foo
>>     t.bar
>>   end
>>
>> -- and:
>>
>>   t.bar if t = foo
>>
>
> Hmm, using a Ruby 1.8.x:
>
> irb(main):001:0> class Foo
> irb(main):002:1>   def name
> irb(main):003:2>     'foo'
> irb(main):004:2>   end
> irb(main):005:1> end
> => nil
> irb(main):006:0> foo = Foo.new
> => #<Foo:0x2be07f0>
> irb(main):007:0> bar.name if bar = foo
> NameError: undefined local variable or method `bar' for main:Object
>         from (irb):7
> irb(main):008:0> bar = nil
> => nil
> irb(main):009:0> bar.name if bar = foo
> => "foo"
>
> Seems like the same "reading ahead of itself" problem of trying to do
> the whiteout quiz on a file without perfect syntax. Example:
>
> irb(main):012:0> 89u33@$T$#$b if false
> SyntaxError: compile error
> (irb):12: syntax error
> 89u33@$T$#$b if false
>      ^
>         from (irb):12
>
> Should you get a syntax error on code never called?

Yes, of course!  Syntax analysis comes before execution.  Every
programming language (whether compiled or interpreted) needs at least
syntactic correct input.

And btw: don't trust IRB when it comes to local variables!

Kind regards

    robert